Controlling movement of automated fixtures can be done using linear movement of the type that is produced by linear actuators. Linear actuators can be driven by various mechanisms, including electric, pneumatic or hydraulic actuators. Linear actuators work by extending and retracting a thrust member, sometimes with a work piece affixed to its end to perform certain tasks A subset of linear actuators, electric ball screw-driven actuators typically include a thrust rod assembly, a screw shaft, a nut, and a work piece connection end, and may further include a housing for the motor and actuator assembly. Within the housing, a motor shaft can be configured to drive the screw shaft. The screw shaft engages the nut coupled with the thrust rod assembly, which transfers rotary motion of the screw shaft into linear motion of the thrust rod assembly. The work piece connection end may support a variety of useful connections depending on the use of the particular actuator. Linear actuators may thus be applied in a variety of uses, such as automated assembly line work to powering animatronics.
A actuators developed for particular applications may have certain strict performance and design requirements. These requirements may include size constraints, operating temperature requirements, or motor performance minimums, among others. Some combinations of these requirements may be desired for a particular actuator assembly. Different requirements may conflict with one another, such as the need for a small total assembly size while also maintaining high performance actuation from a high performance motor. Because electric motors, such as those used to drive actuators, typically have heat output commensurate with their performance, high performance motors in small packages may also have large heat output. As such, operating temperature requirements must be considered as well.
An electric motor normally has a maximum operating temperature limit. Typically, in order to avoid damage to the motor, the motor must be operated within its temperature limit. The operating temperature directly relates to a given amount of current going through the motor, which in turn directly translates to motor output torque. When driving a linear actuator, the motor output torque is converted to a given amount of actuator thrust as the torque is translated through the ball screw and to the work piece of the actuator. As a result of this relationship, the maximum actuator thrust in an actuator assembly is limited by the temperature limit of the motor being used. This can especially be a problem for applications requiring both a high degree of performance in a very small package size, which may hinder heat dissipation. Because when larger servo motors are required to create the same amount of torque as a smaller motor, a larger servo motor will run cooler because it has less resistance, which equates to less power losses.
Thus, there exists a need in the art for a compact screw-driven linear actuator assembly and housing with high performance and torque, combined with improved heat dissipation qualities.